For the first time, researchers have identified how cabbage looper caterpillars in the field develop resistance to the bacterium Bacillus thuringiensis (Bt), which naturally occurs in the soil and on plants and has been developed into the most successful and widely used biological insecticide.

When ingested, the insecticidal toxins in Bt kill insects by destroying their guts. Insects in the field develop resistance to it, however, via a genetic mechanism that alters a toxin receptor in the insect’s gut, two Cornell researchers have discovered. The receptor belongs to a class of digestive enzymes called aminopeptidase N (APN), two of which undergo changes when cabbage loopers develop resistance to Bt on crops.